The present invention is directed to a method of and apparatus for continuously fabricating laminates formed of several layers of resin-impregnated material webs by pressure molding the layers together and including removing the material webs free of resin from a source. The material webs are impregnated with a resin and then cured and dried and the resin is prehardened before passing the combined webs through a pressing zone of a double band press.
Laminates or layered materials are made up of several layers of material webs impregnated with thermosetting plastics material resin and pressure molded together in the desired sequence. Fiber or fabric webs are used as the material webs. Thermosetting resins usable for impregnating the webs are melamine, urea, phenolic, and epoxy resins or the like.
Such laminates can be used as decorative surface coverings for chip board. Decorative laminates include a core and a surface layer and the layers are composed of melamine or phenolic resin-impregnated papers. The surface layer deposited on the core layer is provided with a decorative imprint, such as an imitation wood grain.
In technical applications, laminates can be copper-covered or coated laminates serving as the initial material for the formation of printed circuit boards. Such copper-covered laminates are constructed of a core of several layers of glass cloth impregnated with an epoxy resin. An electrolytically deposited copper foil is placed on the surfaces of the core and is pressed molded together with it. Paper layers impregnated with phenolic resin can also be used as the core material.
In addition, there are laminates where the individual layers are impregnated with a thermoplastic resin. Such layers are arranged in a desired sequence, heated, press molded together and, subsequently, cooled. While thermosetting resins are cured by heat or chemical reaction, thermoplastic resins cure through cooling.
A method of and an apparatus for fabricating decorative laminates is disclosed in DE-AS 27 22 262. In this method, paper free of resin, is removed from rollers and passed through an impregnating device. Thermosetting resin, prehardened to a certain degree, is located in the impregnating device and is maintained in the liquid state, the so-called A-state, by means of solvents and water. The fiber matrix of the paper web is impregnated with the resin in the impregnating device. Subsequently, the resin-impregnated paper web is moved through a drying tunnel where a portion of the solvents and water contained in the resin is evaporated out of the paper web by applying heat. Due to the application of heat, the resin hardens or cures up to a maximum of the B-state. Subsequently, the paper webs are stacked in a desired manner and introduced into a double band press and press molded together along with the application of heat. The resin finally hardens to the C-state in the double band press and joins the individual layers into a compact laminate. After leaving the double band press, the laminated webs are cooled, ground and, subsequently, wound on rollers. The apparatus as shown in the patent publication includes a double band press with take-off rollers for the paper webs located at the press inlet where the conventional impregnating device and drying tunnel are located.
This known device has the disadvantage, because of the arrangement of the impregnating and drying processes upstream of the pressure molding operation and the double band press, that the over-all length of the double band press installation is greatly increased. The resin-impregnated paper webs leaving the impregnating means are very prone to tear and, therefore, are very difficult to control over the long distance from the take-off location to the inlet of the double band press. This known and desirable method, because it is a single-stage method, has not been able to prevail against the two-stage method, where the paper webs are impregnated with resin, dried and, subsequently, again wound on rollers and are pressure-molded into a laminate, only in a second stage in the double band press.
Further, in this known method, it is also disadvantageous that the paper webs are very tacky after leaving the impregnating means and, as a result, cannot be supported and guided. Therefore, an intensive drying process in the drying tunnel is necessary, so that the paper web can advance unsupported to the inlet of the double band press. Such intensive heating, however, involves the danger of additional hardening or curing of the resin beyond the B-state. In addition, heating of the resin impregnated paper webs is required in the double band press to return the resin into a molten state, whereby a good interconnection can be achieved between the individual webs of the laminate. This heating step requires an additional supply of energy. Since the impregnation procedure is already terminated in the drying tunnel, resins rich in solvents and water must be used, to achieve a sufficient impregnation of the fiber matrix of the paper web. These solvents and water must be subsequently removed from the paper web in the drying tunnel, requiring additional energy. Moreover, the escaping solvent vapors result in considerable environmental problems and must be carried away by expensive installations.
A device for metering and applying resins for the impregnation of paper webs, and, particularly suitable for double band presses, is disclosed in DE -PS 31 14 592. This metering and applying device can be used in place of the conventional impregnating device disclosed in DE-AS 27 22 262. The metering and applying device is also arranged upstream of the double band press. This patent publication, however, cannot supply any suggestion to a person skilled in the art for the elimination of the above-mentioned disadvantages.